Aqueous lime slurry, preparation process and uses

Abstract

Preparation of aqueous slurries of calcium dihydroxide. Preparation of aqueous suspensions of calcium hydroxide.

Claims

1. An aqueous slurry of calcium hydroxide comprising water, calcium hydroxide, and a copolymer, said slurry having a dry content of at least 40% by weight, the viscosity of said aqueous slurry as measured by a Brookfield DVIII viscometer at 10 RPM being between 25 and 1,000 mPa.Math.s at 20 C., wherein said copolymer consists: of methacrylic acid monomers and/or any of its salts, optionally of acrylic acid monomers and/or any of its salts, of one or more monomers with the formula (I):
RXR(I) where: R represents a polymerizable unsaturated group, R represents hydrogen or an alkyl group with from 1 to 4 carbon atoms, X represents a structure with n unit(s) of ethylene oxide EO and m unit(s) of propylene oxide PO, arranged randomly or regularly, and m and n are independent non-zero integers and are between 1 and 150, and wherein said slurry is prepared by a process comprising: agitating a mixture of the water and the copolymer to form an aqueous solution; adding the calcium hydroxide in powdered form to said aqueous solution and agitating to provide an initial slurry; applying a homogeneous shear level greater than 50,000 s.sup.1 to the initial slurry; and optionally, while applying said shear level to said initial slurry, adding more copolymer and/or more powdered calcium hydroxide to said initial slurry.

2. The aqueous slurry according to claim 1, wherein the copolymer has a molecular mass between 30,000 and 200,000 g/mol as determined by Gel Permeation Chromatography (GPC).

3. The aqueous slurry according to claim 1, wherein the monomer of formula (I) is such that n+m>17.

4. The aqueous slurry according to claim 1, wherein the R group of said monomer of formula (I) represents the methacrylate group.

5. The aqueous slurry according to claim 1, wherein the R group of the monomer of formula (I) represents H or CH.sub.3.

6. The aqueous slurry according to claim 1, wherein the monomer of formula (I) consists of, expressed as a percentage by weight of each of its components: 5 to 30% by weight of methacrylic acid monomers and/or any of its salts, 0 to 10% by weight of acrylic acid monomers and/or any of its salts, 70 to 95% by weight of monomers of formula (I).

7. The aqueous slurry according to claim 1, wherein a mixer of the rotor-stator type is used to apply said shear.

8. The aqueous slurry according to claim 1, wherein the shear is applied in a device equipped with a recirculating loop.

9. The aqueous slurry according to claim 1, wherein the shear is applied in a device configured to deliver an output of at least 1,000 W/m.sup.3.

10. The aqueous slurry according to claim 1, wherein the R group of said monomer of formula (I) represents an acrylate, methacrylate, methacrylurethane, vinyl or allyl group.

11. A method of treating industrial smoke, domestic wastewater, or industrial wastewater, comprising contacting said smoke or wastewater with the aqueous slurry according to claim 1.

12. A method of flue gas desulfurization, comprising contacting industrial smoke with the aqueous slurry according to claim 1.

13. A process for the preparation of the aqueous slurry of calcium hydroxide of claim 1, the process comprising: agitating a mixture of the water and the copolymer to form an aqueous solution; adding the calcium hydroxide in powdered form to said aqueous solution and agitating to provide an initial slurry; applying a homogeneous shear level greater than 50,000 s.sup.1 to the initial slurry; and optionally, while applying said shear level to said initial slurry, adding more copolymer and/or more powdered calcium hydroxide to said initial slurry.

14. A process according to claim 13, wherein said process comprises adding more copolymer and/or more powdered calcium hydroxide to said initial slurry while applying said shear level to said initial slurry.

Description

EXAMPLES

(1) In all the tests that follow, the slurries are evaluated using the parameters described below.

(2) The viscosity (expressed in mPa.Math.s) of each slurry is measured at 20 C. with a Brookfield DVIII type viscometer. The indicated viscosity values are measured before agitation or after agitation at a speed of 10 RPM and 100 RPM, and at different storage times. The viscosity values after 1 month of storage and after agitation of the slurry (using equipment of the Rayneri type, for example) are all particularly relevant in assessing the characteristics of the invention (influence of the polymer, influence of the equipment, influence of the minimum degree of shearing) with regard to the use of the slurries in industrial processes.

(3) The sedimentation of each slurry is evaluated by a measurement of the height of the deposit in the container. The sedimentation values are expressed in %, that is, the height of the deposit compared to the total height of the slurry in the container, multiplied by 100.

Example 1

(4) This example illustrates the use of different polymers (prior art, invention, outside of the invention) in a process for the preparation of an aqueous slurry of calcium hydroxide (slaked lime) according to the invention.

(5) Several aqueous slurries of calcium hydroxide, each having a 481% solids content, are prepared in this example. 503 g of water are introduced into a container together with a quantity of a polymer corresponding to 1.41% by dry weight (on the basis of the total weight of the solids in the slurry), the said polymer being a polymer of the prior art or a polymer of the present invention. Then, 485 g of slaked lime (Supercalco 97, Carmeuse) are introduced into the container under agitation.

(6) A mixer of the IKA Magic Lab type, adjusted to produce a shearing of 82,000 s.sup.1 is then supplied with the mixture obtained in the previous step. A recirculating loop allows several passages through the gap formed by the rotor and the stator of the IKA mixer.

(7) Once it is sheared, the slurry is stored for an evaluation of its parameters of viscosities, sedimentation and stability at 1 month.

(8) The polymers used in example 1 have the following characteristics:

(9) Test 1-1:

(10) This test demonstrates the use, in a process according to the invention, of a homopolymer outside of the invention available commercially under the name Rheosperse 3010, Coatex, France, and composed of acrylic acid monomers, 100% neutralized with sodium hydroxide (molecular weight): 4,000 g/mol).

(11) Test 1-2:

(12) This test demonstrates the use, in a process according to the invention, of a copolymer outside of the invention commercially available and consisting of acrylic acid monomers and of vinyl-PEG.sub.2000 structured macromonomers, i.e., of monomers having 46 units of ethylene oxide.

(13) Thus, this comb-structured polymer does not, on the one hand, have methacrylic acid monomers, and on the other, propylene oxide units on its macromonomers.

(14) Test 1-3:

(15) This test demonstrates the use, in a process according to the invention, of a commercially available copolymer outside of the invention consisting of 15% by weight of acrylic acid monomers and methacrylic acid monomers, as well as 85% by weight of MPEG.sub.5000 macromonomers (i.e. methoxy (EO).sub.113 units).

(16) Thus, this comb structured polymer does not have propylene oxide units on its macromonomers.

(17) Tests 1-4 to 1-8: copolymers with a particular structure, according to the invention or outside of the invention.

(18) These tests demonstrate the use of water-soluble copolymers according to the invention or outside of the invention, having: a negatively charged skeleton consisting of randomly polymerized acrylic acid and/or methacrylic acid monomers, and uncharged side chains consisting of poly(alkylene glycol) units.

(19) *Test 1-4: Outside of the Invention

(20) The copolymer has the following composition (in % by weight relative to the total weight of the copolymer): 12.8% acrylic acid monomers, 87.2% monomers of formula (I): RXR in which R represents a methacrylate group, R designates hydrogen, X represents a structure with 46 units of ethylene oxide EO and 15 units of propylene oxide PO, arranged randomly.

(21) Molecular weight: 38,000-52,000 g/mol.

(22) Partial NaOH neutralization; pH: 3-4.5.

(23) This copolymer, not having methacrylic acid monomers, is a copolymer outside of the invention.

(24) *Test 1-5: According to the Invention

(25) The copolymer has the following composition (in % by weight relative to the total weight of the copolymer): 7.44% methacrylic acid monomers, 92.56% monomers of formula (I): RXR in which R represents a methacrylate group, R designates hydrogen, X represents a structure with 46 units of ethylene oxide EO and 15 units of propylene oxide PO, arranged randomly.

(26) Molecular weight: 110,000-150,000 g/mol.

(27) Partial NaOH neutralization; pH: 3-4.5.

(28) *Test 1-6: According to the Invention

(29) The copolymer has the following composition (in % by weight relative to the total weight of the copolymer): 19.8% methacrylic acid monomers, 3% acrylic acid monomers, and 77.2% monomers of formula (I): RXR in which R represents a methacrylate group, R designates hydrogen, X represents a structure with 46 units of ethylene oxide EO and 15 units of propylene oxide PO, arranged randomly.

(30) Molecular weight: 34,000-44,000 g/mol.

(31) Total NaOH neutralization; pH: 7.7.

(32) *Test 1-7: According to the Invention

(33) The copolymer has the following composition (in % by weight relative to the total weight of the copolymer): 12.5% methacrylic acid monomers, 87.5% monomers of formula (I): RXR in which R represents a methacrylate group, R designates hydrogen, X represents a structure with 46 units of ethylene oxide EO and 15 units of propylene oxide PO, arranged randomly.

(34) Molecular weight: 60,000-95,000 g/mol.

(35) Total NaOH neutralization; pH: 6.7-7.7.

(36) *Test 1-8: Outside of the Invention

(37) The copolymer has the following composition (in % by weight relative to the total weight of the copolymer): 24% methacrylic acid monomers, 4.3% acrylic acid monomers, and 71.7% monomers of formula (I): RXR in which R represents a methacrylate group, R designates H, X represents a structure with 46 units of ethylene oxide EO.

(38) Neutralization: 100% NaOH.

(39) Molecular weight: 17,900 g/mol.

(40) This copolymer, whose monomers of formula (I) do not have propylene oxide units, is a copolymer outside of the invention.

(41) The results of sedimentation and of the different measurements of viscosity are presented in table 1 below:

(42) TABLE-US-00001 TABLE 1 viscosity viscosity viscosity viscosity viscosity viscosity aftag befag befag aftag aftag aftag T0 T0 + 1 m T0 + 1 m T0 + 1 m T0 + 1m sedimentation T010 100 10 100 10 100 Tests T0 RPM RPM RPM RPM RPM RPM 1-1 PA 15% 10 58 1000 124 2770 382 1-2 PA 0 9840 1140 21000 4550 11020 1146 1-3 PA 0 1940 386 17800 3820 7220 1000 1-4 OI 0 290 170 19000 3310 16460 1900 1-5 INV 0 300 159 4620 890 590 230 1-6 INV 0 250 152 1320 478 730 234 1-7 INV 0 170 114 1260 462 330 170 1-8 OI 30% 30 40 1900 802 470 202 PA: prior art OI: outside of the invention INV: Invention Aftag: after agitation Befag: before agitation

(43) Firstly, one can observe that the polymers of tests 1-1 (homopolymers of acrylic acid) and 1-8 (copolymers with no propylene oxide in their side chains) do not avoid sedimentation. The use of these polymers therefore does not solve the technical problem at the origin of the present invention.

(44) The measurement of viscosity at 10 RPM after agitation and at TO shows that the polymers of tests 1-2 and 1-3 do create slaked lime slurries with rheological characteristics enabling their uses in industrial processes, in particular the rheological characteristics specific to the pumping of the slurries. The slurry obtained in test 1-2 using a polymer of the prior art in fact has a viscosity of 9,840 mPa.Math.s at T0 after agitation. The slurry obtained in test 1-3 using another polymer of the prior art has a viscosity of 1,940 mPa.Math.s at T0 after agitation. These values, outside the range of viscosities claimed (between 25 and 1,000 mPa.Math.s at 20 C.) are incompatible with the use of expected slurries.

(45) The measurement of viscosity at 10 RPM after agitation at T0+1 month shows that the polymer of test 1-4 does not produce a concentrated lime slurry that has a suitable viscosity. In fact, this viscosity rises to 16,460 s.sup.1.

(46) The rheological profiles of the lime slurries of tests 1-5, 1-6 and 1-7 (use of a copolymer according to the invention) are suitable for the use of slurries in industrial processes.

Example 2

(47) This example demonstrates the use of shearing equipment, identical or different, possibly adjusted to different shear levels to prepare an aqueous slurry of calcium hydroxide (slaked lime) containing a copolymer according to the invention.

(48) A first series of three aqueous slurries of calcium hydroxide (tests 2-1 to 2-3), each one having a 481% solids content, is prepared by the introduction into a container of 503 g of water and of a quantity of a polymer which corresponds to 1.41% by dry weight (on the basis of the total weight of the solids in the slurry). The said copolymer is the one of test 1-5. Then, 485 g of slaked lime (Supercalco 97, Carmeuse) are introduced into the container under agitation.

(49) A second series of three aqueous slurries of calcium hydroxide (tests 2-4 to 2-6), each one having a 481% solids content, are prepared by the introduction into a container of 503 g of water and a quantity corresponding to 1.41% by dry weight of a polymer (on the basis of the total weight of the solids in the slurry), the said polymer being that of test 1-6. Then, 485 g of slaked lime (Supercalco 97, Carmeuse) are introduced into the container under agitation.

(50) Tests 2-1 and 2-4

(51) A mixer of the Ultraturax type (rotor-stator type) adjusted to produce a shear of about 40,000 s.sup.1, and which produces a homogeneous shearing according to the definition of the present invention, is supplied with the mixture obtained in the previous step.

(52) A recirculation loop allows several passes through the mixer. The recirculation time is set to 15 minutes.

(53) Tests 2-2 and 2-5

(54) A mixer of the Rayneri type, adjusted to produce a shear of about 3,000 s.sup.1, (which does not produce a homogeneous shearing according to the definition of the present invention), is supplied with the mixture obtained in the previous step.

(55) A recirculation loop allows several passes through the mixer. The recirculation time is set to 15 minutes.

(56) Tests 2-3 and 2-6

(57) A mixer of the IKA Magic Lab type, adjusted to produce a shear of about 82,000 s.sup.1, and which produces a homogeneous shearing according to the definition of the present invention, is then supplied with the mixture obtained in the previous step.

(58) A recirculating loop allows several passages through the gap formed by the rotor and the stator of the IKA mixer. The recirculation time is set to 15 minutes.

(59) Once they are sheared, the slurries are stored for an evaluation of the parameters of viscosities, sedimentation and stability at 1 month.

(60) The results of sedimentation and of the different measurements of viscosity are presented in table 2 below:

(61) TABLE-US-00002 TABLE 2 viscosity viscosity viscosity viscosity Aftag Aftag viscosity befag viscosity aftag T0 T0 befag T0 + 1 m aftag T0 + 1 m sedimentation 10 100 T0 + 1 m 100 T0 + 1 m 100 Tests T0 RPM RPM 10 RPM RPM 10 RPM RPM 2-1 OI 30% 70 107 3300 560 430 168 2-2 OI 20% 50 98 2400 236 790 220 24 INV 0 300 159 4620 890 590 230 24 OI 30% 650 162 1600 580 1890 380 2-5 OI 30% 260 107 19300 1800 1000 240 2-6 INV 0 250 152 1320 478 730 234 OI: outside of the invention INV: Invention Aftag: after agitation Befag: before agitation

(62) It is immediately apparent that the shear level used in tests 2-1 and 2-4 (Ultraturax adjusted to 40,000 s.sup.1) and tests 2-2 and 2-5 (3,000 s.sup.1 mixer) do not avoid sedimentation.

(63) On the other hand, the shear level of tests 2-3 and 2-6 (IKA adjusted to 82,000 s.sup.1), combined with the use of a polymer with a particular structure, not only avoids the problem of sedimentation, but in addition, enables the production of slurries whose rheological profile is adapted to the expected use.

Example 3

(64) This example illustrates the use of two polymers according to the invention in a process for the preparation of an aqueous slurry of calcium hydroxide (slaked lime) with a high dry extract content (>50% by weight).

(65) Two aqueous slurries of calcium hydroxide, each having a 50 to 51% solids content, are prepared in this example. 478 g of water are introduced into a container together with a quantity of a polymer corresponding to 1.41% by dry weight, on the basis of the total weight of the solids in the slurry. Then, 505 g of slaked lime (Supercalco 97, Carmeuse) are introduced into the container under agitation.

(66) A mixer of the IKA Magic Lab type, adjusted to produce a shearing of 82,000 s.sup.1 is then supplied with the mixture obtained in the previous step. A recirculating loop allows several passages through the gap formed by the rotor and the stator of the IKA mixer.

(67) Once it is sheared, the slurry is stored for an evaluation of its parameters of viscosity, sedimentation and stability at 1 month.

(68) The polymers used in this example have the following characteristics:

(69) Test 3-1: According to the Invention

(70) The copolymer has the following composition (in % by weight relative to the total weight of the copolymer): 7.44% methacrylic acid monomers, 92.56% monomers of formula (I): RXR in which R represents a methacrylate group, R designates hydrogen, X represents a structure with 46 units of ethylene oxide EO and 15 units of propylene oxide PO, arranged randomly.

(71) Molecular weight: 110,000-150,000 g/mol.

(72) Partial NaOH neutralization; pH: 3-4.5.

(73) Test 3-2: According to the Invention

(74) The copolymer has the following composition (in % by weight relative to the total weight of the copolymer): 19.8% methacrylic acid monomers, 3% acrylic acid monomers, and 77.2% monomers of formula (I): RXR in which R represents a methacrylate group, R designates hydrogen, X represents a structure with 46 units of ethylene oxide EO and 15 units of propylene oxide PO, arranged randomly.

(75) Molecular weight: 34,000-44,000 g/mol.

(76) Total NaOH neutralization; pH: 7.7.

(77) The results of sedimentation and of the different measurements of viscosity are presented in table 3 below:

(78) TABLE-US-00003 TABLE 3 viscosity viscosity viscosity viscosity viscosity viscosity aftag aftag befag befag aftag aftag sedimentation T0 T0 T0 + 1 m T0 + 1 m T0 + 1 m T0 + 1 m Tests T0 10 RPM 100 RPM 10 RPM 100 RPM 10 RPM 100 RPM 3-1 50.4% 0% 980 393 4900 1980 1930 687 lime 50.56% 3-2 lime 0% 530 261 13600 3048 3300 839 Aftag: after agitation Befag: before agitation

(79) The results demonstrate that it is possible, according to the process of the present invention, and using water-soluble copolymers with a particular structure, to prepare high concentration slaked lime slurries that remain stable over time.

Example 4

(80) This example demonstrates the use of two polymers according to the invention in a process for the preparation of an aqueous slurry of calcium hydroxide starting with two different types of slaked lime, namely, a lime with an average particle diameter between 4 and 5 m (Supercalco 97, Carmeuse), and a lime with an average particle diameter between 2 and 3 m (Supercalco 97/20, Carmeuse).

(81) Several aqueous slurries of calcium hydroxide, each having a 481% solids content, are prepared in this example. 503 g of water are introduced into a container together with a quantity of a polymer corresponding to 1.41% by dry weight (on the basis of the total weight of the solids in the slurry). Then, 485 g of slaked lime, specifically, Supercalco 97 (Carmeuse) in tests 4-1 and 4-3, or Supercalco 97/20 (Carmeuse) in tests 4-2 and 4-4, are introduced into the container under agitation.

(82) A mixer of the IKA Magic Lab type, adjusted to produce a shearing of 82,000 s.sup.1 is then supplied with the mixture obtained in the previous step.

(83) A recirculating loop allows several passages through the gap formed by the rotor and the stator of the IKA mixer.

(84) Once it is sheared, the slurry is stored for an evaluation of its parameters of viscosities, sedimentation and stability at 1 month.

(85) The polymers used in this example have the following characteristics:

(86) Tests 4-1 and 4-2: According to the Invention

(87) The copolymer has the following composition (in % by weight relative to the total weight of the copolymer): 7.44% methacrylic acid monomers, 92.56% monomers of formula (I): RXR in which R represents a methacrylate group, R designates hydrogen, X represents a structure with 46 units of ethylene oxide EO and 15 units of propylene oxide PO, arranged randomly.

(88) Molecular weight: 110,000-150,000 g/mol.

(89) Partial NaOH neutralization; pH: 3-4.5.

(90) Tests 4-3 and 4-4: according to the invention

(91) The copolymer has the following composition (in % by weight relative to the total weight of the copolymer): 19.8% methacrylic acid monomers, 3% acrylic acid monomers, and 77.2% monomers of formula (I): RXR in which R represents a methacrylate group, R designates hydrogen, X represents a structure with 46 units of ethylene oxide EO and 15 units of propylene oxide PO, arranged randomly.

(92) Molecular weight: 34,000-44,000 g/mol.

(93) Total NaOH neutralization; pH: 7.7.

(94) The results of sedimentation and of the different measurements of viscosity are presented in table 4 below:

(95) TABLE-US-00004 TABLE 4 Viscosity Viscosity Sedimentation AFTAG AFTAG T0 Tests T0 10 RPM 100 RPM 4-1 INV 0% 300 159 4-2 INV 0% 280 203 4-3 INV 0 250 152 4-4 INV 0% 190 126 Aftag: after agitation Befag: before agitation

(96) The results demonstrate that it is possible, according to the process of the present invention, by using water-soluble copolymers with a particular structure, to prepare high concentration slaked lime slurries that remain stable over time, regardless of the starting particle size distribution of the slaked lime.

Example 5

(97) The purpose of this example is to illustrate the levels of total organic carbon (TOC) present in the aqueous phase of lime slurries dispersed with the polymers of the prior art or with the polymers of the invention, and thus determine the concentrations of free polymers in the aqueous phase.

(98) This example helps to illustrate the levels of soluble Ca.sup.2+ ions present in the aqueous phase of lime slurries dispersed with polymers of the prior art or with polymers of the invention.

(99) Process for the Preparation of Slurries

(100) Several aqueous slurries of calcium hydroxide, each having a 481% solids content, are prepared in this example. 503 g of water are introduced into a container together with a quantity of a polymer corresponding to 1.41% by dry weight (on the basis of the total weight of the solids in the slurry), the said polymer being according to the prior art or according to the present invention. Then, 485 g of slaked lime (Supercalco 97, Carmeuse) are introduced into the container under agitation.

(101) A mixer of the IKA Magic Lab type, adjusted to produce a shearing of 82,000 s.sup.1 is then supplied with the mixture obtained in the previous step. A recirculating loop allows several passages through the gap formed by the rotor and the stator of the IKA mixer.

(102) Test 5-1

(103) The copolymer has the following composition (in % by weight relative to the total weight of the copolymer): 7.44% methacrylic acid monomers, 92.56% monomers of formula (I): RXR in which R represents a methacrylate group, R designates hydrogen, X represents a structure with 46 units of ethylene oxide EO and 15 units of propylene oxide PO, arranged randomly.

(104) Molecular weight: 110,000-150,000 g/mol.

(105) Partial NaOH neutralization; pH: 3-4.5.

(106) Test 5-2

(107) The copolymer has the following composition (in % by weight relative to the total weight of the copolymer): 12.8% acrylic acid monomers, 87.2% monomers of formula (I): RXR in which R represents a methacrylate group, R designates hydrogen, X represents a structure with 46 units of ethylene oxide EO and 15 units of propylene oxide PO, arranged randomly.

(108) Molecular weight: 38,000-52,000 g/mol.

(109) Partial NaOH neutralization; pH: 3-4.5.

(110) This copolymer, not having methacrylic acid monomers, is a copolymer outside of the invention.

(111) Test 5-3

(112) The polymer used is a homopolymer outside of the invention available commercially under the name Rheosperse 3010, Coatex, France, and composed of acrylic acid monomers, 100% neutralized with sodium hydroxide (molecular weight: 4,000 g/mol).

(113) The slurries obtained are filtered.

(114) A sample of the filtrate is taken and analysed according to the methods described below.

(115) Measurement of TOC:

(116) The TOC (Total Organic Carbon) is measured using a Shimadzu TOC-V CSH by means of a method based on a catalytic oxidation by combustion method at 680 C.

(117) The carbon atoms of the samples are oxidized into CO.sub.2. The gas eluent pushes the CO.sub.2 into a system that enables the removal of H.sub.2O molecules and halogenated compounds. An IR detector measures the CO.sub.2 concentration. A calibration curve is used to determine the carbon concentration in the sample.

(118) Assay of Ions:

(119) The ion content is evaluated by means of ion chromatography using Metrohm 761 Compact IC type equipment. Separation of ions and polar molecules is based on their charge.

(120) The results of TOC and free Ca.sup.2+ ion concentration measurements are given in table 5 below:

(121) TABLE-US-00005 TABLE 5 Tests Ca2+ ppm TOC ppm polymer concentration ppm 5-1 INV 1064 1640 396 5-2 OI 995 3900 856 5-3 PA 291 100 17

(122) It is observed firstly that the levels of free Ca.sup.2+ ions vary significantly depending on the nature of the polymer used. This free Ca.sup.2+ ion content in a lime slurry dispersed with an acrylic acid homopolymer (test 5-3) is low compared to that of an aqueous slurry of lime dispersed with a copolymer with a (meth)acrylic acid skeleton and poly(alkyleneglycol) side chains (tests 5-1 and 5-2).

(123) In addition, although the starting quantities of polymer (1.41% by dry weight) are identical for each of the slurries, it is noted that the concentrations of polymer in the filtrate of each slurry vary significantly depending on the polymer used. When the polymer used is an acrylic acid homopolymer, the concentration of soluble polymer in the aqueous phase is almost zero. In addition, there is less free copolymer in the lime slurry filtrate when using a copolymer according to the invention. Without being bound to any theory, one can think that the particular structure of the copolymer according to the invention is adapted to the chemical nature of lime, which improves the chemical interactions between the copolymer and the particles of Ca(OH).sub.2. There is less free copolymer in the lime slurries prepared according to the process of the invention by using a copolymer with a particular structure, because a greater quantity of it is adsorbed on the surface of the slaked lime particles. It is thus shown that submitting a concentrated aqueous lime slurry to a shearing operation under specific conditions in the presence of a copolymer according to the invention produces a concentrated, stable lime slurry which is novel compared to lime slurries of the prior art by virtue of the specific chemical interactions between the copolymers and lime particles.

(124) Embodiment 1.Process for the preparation of an aqueous slurry of calcium hydroxide with a dry content of at least 40% by weight, the viscosity of the said aqueous slurry measured by a Brookfield DVIII viscometer at 10 RPM being between 25 and 1,000 mPa.Math.s at 20 C., including the steps consisting of: a) the availability of a specific volume of an aqueous solution, b) the availability of a measured quantity of powdered calcium hydroxide, c) the availability of a specified quantity of a copolymer consisting: of methacrylic acid monomers and/or any of its salts, possibly of acrylic acid monomers and/or any of its salts, monomers with the formula (I):
RXR (I)
according to which: R represents a polymerisable unsaturated group, notably acrylate, methacrylate, methacrylurethane, vinyl or allyl, R represents hydrogen or an alkyl group with from 1 to 4 carbon atoms, X represents a structure with n unit(s) of ethylene oxide EO and m unit(s) of propylene oxide PO, arranged randomly or regularly, m and n are 2 non-zero integers and are between 1 and 150, d) to at least a part of said aqueous solution, at least a part of the quantity of the said copolymer is added under agitation, e) to the aqueous solution of step d), at least a part of the said quantity of the said calcium hydroxide is added under agitation, f)) a homogeneous shear level greater than 50,000 s.sup.1 is applied to the mixture resulting from step e), g) possibly, in the course of step f), the remaining quantity of the said copolymer and/or of the said calcium hydroxide is added.

(125) Embodiment 2. Process according to Embodiment 1, according to which the copolymer has a molecular mass between 30,000 and 200,000 g/mol as determined by Gel Permeation Chromatography (GPC).

(126) Embodiment 3. Process according to any of the preceding Embodiments, according to which the said monomer of formula (I) is such that n and m are two non-zero integers, and n+m>17.

(127) Embodiment 4. Process according to any of the preceding Embodiments, according to which the R group of the said monomer of formula (I) represents the methacrylate group.

(128) Embodiment 5. Process according to any of the preceding Embodiments, according to which the R group of the said monomer of formula (I) represents H or CH.sub.3.

(129) Embodiment 6. Process according to any of the preceding Embodiments, according to which the said monomer of formula (I) consists of, expressed as a percentage by weight of each of its components: 5 to 30% by weight of methacrylic acid monomers and/or any of its salts, 0 to 10% by weight of acrylic acid monomers and/or any of its salts, 70 to 95% by weight of monomers of formula (I).

(130) Embodiment 7. Process according to any of the preceding Embodiments, according to which a mixer of the rotor-stator type is used for step f).

(131) Embodiment 8. Process according to any of the preceding Embodiments, according to which the device used to perform the step f) is equipped with a recirculating loop.

(132) Embodiment 9. Process according to any of the preceding Embodiments, according to which a device configured to deliver a useful output of at least 1,000 W/m.sup.3 is used to carry out step f).

(133) Embodiment 10. Aqueous slurry of calcium hydroxide with a dry content of at least 40% by weight, the viscosity of the said aqueous slurry measured by a Brookfield DVIII viscometer at 10 RPM being between 25 and 1,000 mPa.Math.s at 20 C., the said slurry being likely to be obtained by the process according to any of claims 1 to 9.

(134) Embodiment 11. Use of a slaked lime aqueous slurry according to Embodiment 10 for the treatment of industrial smoke, including for the desulfurization of smoke, or for the treatment of domestic wastewater, including drinking, or industrial wastewater.

(135) Use of a Hydrosoluble Copolymer to Produce an Aqueous Suspension of Lime.

(136) The present invention as further described hereinbelow also relates to the technical field of the preparation of aqueous suspensions of calcium hydroxide. More specifically, the present invention relates to the use of a hydrosoluble copolymer to prepare a lime-based suspension, as well as aqueous suspensions of lime comprising such a polymer. Such suspensions are in particular used as a chemical neutralizing agent in industrial or household methods.

(137) Calcium hydroxide Ca(OH).sub.2, also called slaked lime or hydrated lime, is obtained by hydrating calcium oxide CaO, also called quicklime, according to the following exothermic reaction: CaO+H.sub.2O.fwdarw.Ca(OH).sub.2.

(138) In the context of the present invention as further described hereinbelow, the terms calcium hydroxide or calcium dihydroxide are used equivalently to designate particles of Ca(OH).sub.2.

(139) Calcium hydroxide-based products assume various forms: powdered (dry, powdery form), plastic pastes, or aqueous suspensions-dispersions (milk of lime).

(140) The invention as further described hereinbelow more particularly relates to a calcium hydroxide-based product found in the form of an aqueous suspension. Such aqueous slaked lime suspensions may be used as chemical neutralizing agents in many industrial methods. Examples include industrial effluent treatment, for example gaseous effluents such as acid fumes. Examples also include the treatment of potable water, wastewater or industrial water.

(141) Aqueous suspensions of slaked lime are in particular characterized by their dry matter content (wt %). One skilled in the art traditionally seeks to increase the dry matter content in aqueous solutions of slaked lime, primarily for economic reasons: by increasing the dry matter content of the aqueous suspensions of slaked lime, transport and handling costs are reduced per ton of product. Furthermore, the annoyances due to the manipulation of powders (hygiene, handling) are reduced and implementation is made easier.

(142) To increase the dry matter content of aqueous suspensions of slaked lime, it is in particular possible to use a dispersing agent.

(143) Dispersing agent refers to an agent that has the ability to improve the dispersion state of the particles of Ca(OH).sub.2 within the aqueous suspension. Concretely, when these agents are used in aqueous suspensions of a mineral material, they cause a decrease in viscosity. Thus, an aqueous suspension of a mineral material including a dispersing agent will have a viscosity lower than that of the same aqueous suspension of mineral material not containing said dispersing agent.

(144) A certain number of prior art documents describe the use of dispersing agents. Document EP 0,061,354 (Blue Circle) describes the use of anionic oligomeric polyelectrolytes, for example methacrylic acid homopolymers, carboxymethylcellulose or sulfonate, to manufacture aqueous dispersions of slaked lime.

(145) Document FR 2,677,351 (Italcementi) describes a concentrated aqueous suspension of calcium hydrate, which contains at least 40% solid hydrated lime obtained from powdered hydrated lime, slaked lime or quicklime, and a hydrosoluble polymer that may be an alkali or alkaline-earth metal polyacrylate.

(146) Document EP 0,594,332 (Rohm & Haas) describes the use of polymeric anionic dispersing agents to obtain dispersions of aqueous quicklime or slaked lime. These dispersing agents are chosen from among homopolymers, copolymers and terpolymers having carboxylic acid, sulfonic acid or phosphoric acid functionalities. The monomers that impart such an acid functionality for example include acrylic acid, methacrylic acid, crotonic acid, maleic acid, maleic anhydride, itaconic acid, mesaconic acid, fumaric acid, citraconic acid, vinylacetic acid, acryloxypropionic acid, vinylsulfonic acid, styrenesulfonic acid, 2-acrylamido-2-methylpropanesulfonic acid, allyl sulfonic acid, allyl phosphonic acid, vinylphosphonic acid, and vinylsulfonic acid.

(147) Document US 2008/0011201 (Ultimate Nominees) describes the combined use of a polycarboxylate dispersant and a carbohydrate dispersant to prepare a milk of lime for applications in the food and potable water field. In particular, according to this document, the carbohydrate dispersant is a sugar, in particular chosen from among aldoses, saccharides, disaccharides and polysaccharides. Also, examples of a polycarboxylate dispersant are in particular the salts of maleic styrene anhydride copolymers or polycarboxylate polyether salts. This document in particular describes the combined use of a comb-type copolymer, in particular Ethacryl G (polycarboxylate dispersant by the company Coatex) and a glucose syrup (carbohydrate dispersant) to prepare a 50% hydrated lime suspension/dispersion.

(148) Document EP 0,848,647 (Chemical L Company) describes the use of a dispersing agent of the anionic polyelectrolyte type, combined with an alkali metal hydroxide, to prepare a lime suspension that may be quicklime or slaked lime. The anionic polyelectrolyte is chosen from among polyacrylic acid, polycarboxylic acid, and polyphosphoric acid, the copolymers of polyacrylic acid, polycarboxylic acid and polyphosphoric acid and their alkali metal salts.

(149) Document FR 6,687,396 (Lhoist) describes a method for slaking CaO or magnesium oxide in the presence of SO.sub.3.sup., SO.sub.4.sup.2 or Cl.sup. ions and in that during or at the end of the reaction, a polymer or copolymer is added comprising monomers chosen from among acrylic acid and its salts, methacrylic acid and its salts, vinylbenzyl sulfonic acid and its salts, acrylamido-2-methylpropanesulfonic acid and its salts, 2-sulfoethyl methacrylate and its salts.

(150) Document JP 09 122471 (Nippon Shokubai) describes the use of copolymers made up of a carboxylic monomer and a monomer of the polyalkylene glycol methacrylate type as dispersing agent making it possible to obtain aqueous dispersions of slaked lime with a low viscosity. This document illustrates the use, to that end, of copolymers having a molecular weight of less than 20,000 g/mol.

(151) Document WO 2010/106111 (Lhoist) relates to compositions comprising slaked lime and/or quicklime and an organic polymer incorporated into the solid phase of the slaked lime. The polymers described in this document may be non-ionic, anionic, cationic or amphoteric and of quite varied natures. They may be obtained from monomers chosen from among anionic monomers having a carboxylic function or a sulfonic acid function, non-ionic monomers (acrylamide, methacrylamide, N-vinyl pyrrolidone, vinyl acetate, vinyl acid, acrylate esters, allyl alcohol, N-vinyl acetamide, N-vinylformamide), cationic monomers (quaternized or salified ADAME or MADAME, DADMAC, APTAC, MAPTAC), optionally combined with one or more hydrophobic monomer(s) preferably chosen from the group comprising the esters of alkyl chain, arylalkyl and/or ethoxylated methacrylic acid, the derivatives of alkyl chain, arylalkyl or dialkyl methacrylamide, the allyl cationic derivatives, the derivatives of anionic or cationic hydrophobic methacryloyl, or the anionic and/or cationic monomers derived from methacrylamide bearing a hydrophobic chain.

(152) In using the polymers of the prior art, the inventors nevertheless observed a problem of sedimentation when the suspensions are kept without agitation for a period exceeding 3 days, in particular during transport thereof. A paste then forms in the bottom of the vats containing the suspensions, which makes it difficult, if not impossible, to pump them.

(153) The inventors further noted that this sedimentation problem was due to a poorly adapted rheology of the suspensions currently available and poor de-agglomeration of the lime particles.

(154) The dispersing agents that are currently available do not make it possible to obtain fully satisfactory suspensions of aqueous lime, in particular in terms of sedimentation and rheological properties.

(155) One aim of the present invention as further described hereinbelow is to avoid the problem of sedimentation when the lime suspensions are kept without agitation.

(156) Another aim of the present invention as further described hereinbelow is to propose aqueous suspensions of lime that are as concentrated as possible and have a rheology suitable for their uses in industrial methods.

(157) Surprisingly, the inventors have shown that by using a polymer with a particular structure, it was possible to obtain concentrated aqueous suspensions that are stable over time.

(158) More specifically, the first aim of the present invention relates to the use of a hydrosoluble copolymer made up of: monomers of methacrylic acid and/or any one of its salts, optionally, monomers of acrylic acid and/or any one of its salts, monomers with formula (I):
RXR (I) wherein: R represents a polymerizable unsaturated function, in particular acrylate, methacrylate, methacryl-urethane, vinyl or allyl, R designates hydrogen or an alkyl group having n unit(s) of ethylene oxide EO and m unit(s) of propylene oxide PO, positioned randomly or regularly,

(159) m and n are two non-zero integers and comprised between 1 and 150, to prepare an aqueous suspension of calcium hydroxide from powdered calcium hydroxide.

(160) The present invention also relates to an aqueous suspension of calcium hydroxide, comprising at least one copolymer made up of: monomers of methacrylic acid and/or any one of its salts, optionally, monomers of acrylic acid and/or any one of its salts, monomers with formula (I):
RXR (I) wherein: R represents a polymerizable unsaturated function, in particular acrylate, methacrylate, methacryl-urethane, vinyl or allyl, R designates hydrogen or an alkyl group having from 1 to 4 carbon atoms, X represents a structure comprising n unit(s) of ethylene oxide EO and m unit(s) of propylene oxide PO, positioned randomly or regularly, m and n are two non-zero integers and comprised between 1 and 150.

(161) The inventors in fact realized that for aqueous suspensions to have the expected properties relative to stability over time and concentration, it was necessary to disperse the calcium hydroxide particles in the presence of a hydrosoluble comb copolymer of having a backbone of methacrylic acid and poly(alkylene glycol) side chains with a particular structure.

(162) Powdered calcium hydroxide refers to slaked lime particles. Slaked lime is a lime made up of a set of solid particles, primarily calcium hydroxide Ca(OH).sub.2, which is the result of the reaction of quicklime particles with water, that reaction being called hydration or slaking. Slaked lime is also called hydrated lime. In general, the slaked lime may contain impurities, which primarily result from the quicklime, for example magnesium, magnesium oxide, Al.sub.2O.sub.3, Fe.sub.2O.sub.3, MgO, S, SiO.sub.2, Mn.sub.3O.sub.4, silicates, etc. Slaked lime may assume a powdered form or take the form of an aqueous suspension, called milk of lime.

(163) In the context of the present invention, the slaked lime is dispersed in powdered form in an aqueous solution so as to obtain a concentrated milk of lime that is stable over time. The starting mineral material may for example be a powdered slaked lime that is commercially available. Examples include the slaked lime sold under the names Supercalco 97, Supercalco 97/20, Sorbacal SP, Standard Hydrated Lime, MicroCal HF.

(164) The particular methacrylic copolymer according to the invention is a hydrosoluble comb copolymer having a backbone of methacrylic acid, and optionally acrylic acid, and poly(alkylene glycol) side chains.

(165) Poly(alkylene glycol) refers to a polymer of the glycol alkylene derived from an olefinic acid.

(166) The poly(alkylene glycol) chains of the copolymer according to the present invention contain a proportion of ethylene-oxy groups and a proportion of propylene-oxy groups. The poly(alkylene glycol) chains according to the present invention may for example comprise a dominant proportion of ethylene-oxy groups associated with a secondary proportion of propylene-oxy groups. Specific examples of glycol alkylene polymers comprise: poly(alkylene glycols) having an average molecular weight of 1000, 4000, 6000, 10,000 and 20,000 g/mol; polyethylene-polypropylene glycols having an ethylene oxide percentage comprised between 20 and 80 wt % and a propylene oxide percentage comprised between 20 and 80 wt %.

(167) It should be noted that the ethylene-oxy groups and the propylene-oxy groups of the side chains of the copolymer may be positioned randomly, regularly or in a block.

(168) More specifically, the polymer according to the present invention is made up of: monomers of methacrylic acid and/or any one of its salts, optionally, monomers of acrylic acid and/or any one of its salts, monomers with formula (I):
RXR (I) wherein: R represents a polymerizable unsaturated function, in particular acrylate, methacrylate, methacryl-urethane, vinyl or allyl, R designates hydrogen or an alkyl group having from 1 to 4 carbon atoms, X represents a structure including n unit(s) of ethylene oxide EO and m unit(s) of propylene oxide PO, positioned randomly or regularly, m and n are two non-zero integers and comprised between 1 and 150.

(169) Thus, the copolymer according to the invention has a backbone made up of methacrylic acid monomers, and optionally acrylic acid monomers. The inventors in fact realized that the presence of methacrylic acid monomers in the backbone of the copolymer according to the invention was essential to resolve the technical problem at the origin of the present invention.

(170) According to one embodiment of the invention, the copolymer has a backbone made up exclusively of methacrylic acid monomers.

(171) According to another embodiment of the invention, the copolymer has a backbone made up of methacrylic acid monomers and acrylic acid monomers.

(172) Thus, in the context of the present invention, it is not possible to use a copolymer having a backbone made up exclusively of acrylic acid monomers.

(173) The inventors further noted that the use, in the context of the present invention, of the comb-type copolymer marketed under the name Ethacryl G (polycarboxylate dispersant by the company Coatex, which does not contain methacrylic acid monomers) is not suitable to resolve the technical problem at the origin of the present invention.

(174) Said copolymer is obtained using the known conventional radical co-polymerization methods in solution, bulk, direct or inverse emulsion, in suspension, or by precipitation in appropriate solvents, in the presence of catalytic systems and known transfer agents, or using controlled radical polymerization methods such as reversible addition-fragmentation transfer (RAFT), atom transfer radical polymerization (ATRP), nitroxide mediated polymerization (NMP), or cobaloxime mediated radical polymerization.

(175) It is obtained in an acid form and optionally distilled. It may also be partially or completely neutralized by one or more neutralizing agents chosen from among sodium, calcium, magnesium and potassium hydroxide and mixtures thereof, or chosen from among the amines.

(176) According to one embodiment of the present invention, said copolymer is 100% neutralized with sodium hydroxide.

(177) According to another embodiment of the present invention, said copolymer is partially neutralized with sodium hydroxide.

(178) According to one embodiment, said aqueous suspension of calcium hydroxide contains a hydrosoluble copolymer concentration that varies between 0.01 and 10 wt %, based on the total weight of calcium hydroxide particles in the suspension.

(179) According to another embodiment, said aqueous suspension of calcium hydroxide contains a hydrosoluble copolymer concentration that varies between 0.05 and 5 wt %, based on the total weight of calcium hydroxide particles in the suspension.

(180) According to still another embodiment, said aqueous suspension of calcium hydroxide contains a hydrosoluble copolymer concentration that varies between 0.1 and 3.0 wt %, based on the total weight of calcium hydroxide particles in the suspension.

(181) According to another embodiment, said aqueous suspension of calcium hydroxide contains a hydrosoluble copolymer concentration that varies between 0.2 and 2.0 wt %, based on the total weight of calcium hydroxide particles in the suspension.

(182) According to another embodiment, the aqueous suspension according to the present invention is made up of an aqueous solutionfor example, water, optionally additivated, calcium hydroxide particles and a copolymer according to the present invention.

(183) According to another embodiment, the aqueous solution according to the present invention is made up of water, particles of calcium hydroxide and a copolymer according to the present invention. According to this embodiment, the aqueous suspension does not comprise any additive other than the copolymer described in the present application, i.e., it does not, for example, comprise another polymer or dispersant.

(184) According to one embodiment, the aqueous suspension is an aqueous suspension containing a dry content of at least 40 wt %, based on the total weight of the aqueous suspension. According to another embodiment, the aqueous suspension according to the present invention has a calcium hydroxide particle content comprised between 40 to 60 wt %, based on the total weight of the aqueous suspension.

(185) The viscosity of said aqueous suspension measured by a Brookfield DVIII viscosimeter being comprised between 25 and 1000 mPa.Math.s at 20 C., said suspension [can] be obtained using the method according to the present invention.

(186) According to another embodiment, the aqueous suspension according to the present invention has a content level of calcium hydroxide particles comprised between 45 to 55 wt %, based on the total weight of the aqueous suspension.

(187) According to one embodiment of the present invention, said copolymer has a molecular weight comprised between 30,000 and 200,000 g/mol as determined by steric exclusion chromatography (SEC).

(188) According to another embodiment of the present invention, the copolymer has a molecular weight comprised between 30,000 and 160,000 g/mol as determined by steric exclusion chromatography (SEC).

(189) According to one embodiment of the present invention, in said hydrosoluble copolymer, said monomer of formula (I) is such that n and m are two non-zero integers and n+m>17.

(190) According to one embodiment of the present invention, in said hydrosoluble copolymer, the function R of said monomer with formula (I) represents the methacrylate function.

(191) According to one embodiment of the present invention, in said copolymer, the function R of said monomer with formula (I) represents H or CH.sub.3.

(192) According to one embodiment of the present invention, in said copolymer, said monomer with formula (I) is made up of, expressed in percentage by weight of each of its components: 5 to 30 wt % monomers of methacrylic acid and/or any one of its salts, 0 to 10 wt % monomers of acrylic acid and/or any one of its salts, 70 to 95 wt % monomers with formula (I).

(193) According to one embodiment of the present invention, in said copolymer, said monomer of formula (I) is made up of, expressed in percentage by weight of each of its components: 7 to 22 wt % monomers of methacrylic acid and/or any one of its salts, 0 to 5 wt % monomers of acrylic acid and/or any one of its salts, 78 to 93 wt % monomers with formula (I).

(194) A third object of the present invention also relates to the use of the aqueous suspension of slaked lime according to the invention in the following applications.

(195) The suspensions may be used in the treatment of power plant fumes for plants using fuels (in particular coal) for example containing sulfur and other impurities that generate acid molecules (sulfur dioxide, sulfur trioxide, sulfuric acid, hydrochloric acid, hydrofluoric acid, etc.) or pollutants (mercury, heavy metals, etc.).

(196) They may also be used in household or industrial waste incineration plants that generate the same types of pollutants, additionally with dioxins. Using lime in a concentrated aqueous suspension, sprayed into the fumes, makes it possible to trap the pollutants, which are then eliminated in the solid residues produced by the reaction with the lime and the partial or total drying of said reaction products.

(197) The suspensions may be used as neutralizing agents for acid reaction products, allowing their elimination and solid and/or neutralized form or their use in the form of calcium salt (for example as neutralized sulfonates and phenates as additives for lubricant products). Non-exhaustively, examples include the neutralization of acid sludge resulting from the manufacture of titanium dioxide, and the neutralization of acid solutions produced during methods for manufacturing chemical products.

(198) The aqueous solutions according to the present invention may be used as neutralizing agents for mining effluents, with the aim of neutralizing the acidity and/or separating the heavy metals in solution before discharging the fluids into the natural environment or lagoon.

(199) The suspensions may be used in water decarbonatation methods, these methods making it possible to reduce the temporary hardness of the water (partial or complete elimination of bicarbonates of the alkaline-earth metals). The water thus treated is intended to be used as potable or industrial water, optionally after readjusting the pH using carbon dioxide or any other acid suitable for the final application.

(200) The purification treatment for potable water, wastewater or industrial water creates residue called sludge. The sludge is first separated from the purified water, then treated so as to stabilize and concentrate it. The method for treating this sludge is generally called conditioning and uses organic and/or mineral additives.

(201) The present invention also relates to the use of the aqueous suspension of slaked lime according to the invention to condition the sludge from wastewater treatment plants. The lime in suspension is used first to favor the flocculation of the sludge, and secondly to sterilize said sludge using the pH by keeping said sludge at a pH of 12 or more for 24 to 72 hours or more.

(202) The suspensions may be used in the treatment of aggregates used during the production of bituminous coatings. The adhesion of the bituminous emulsions on the aggregates is greatly improved when these aggregates are treated beforehand using lime. This better adhesion leads to bituminous coatings that are more resistant to wear and deformation, and which have a prolonged physical integrity.

(203) The aqueous solutions according to the present invention can be used to produce construction materials such as cellular concrete. The lime is mixed with cement, sand and aluminum powder. The high pH of the mixture causes a gaseous release of hydrogen by etching of the aluminum, and the aerated paste thus produced is molded, then autoclaved to create parts made from cellular concrete.

(204) The aqueous solutions of the present invention may be used in the treatment of contaminated soils so as to neutralize the acidity of the soils, immobilize the pollutants by neutralization or flocculation, and thereby prevent the pollutants from reaching the groundwater.

(205) The aqueous suspensions of the present invention may be used in the treatment of agricultural soils so as to correct the pH of those soils, enrich said soils by contributing a calcium or calcium magnesium source in the case of dolomitic limes, and make those soils less impermeable by flocculation of the clays that they contain.

(206) The aqueous solutions of the present invention may be used in the treatment of surface waters, lakes, ponds and rivers for the purpose of adjusting the pH of the water to reduce the impact of the acidification of said water, acidification of pluvial or animal origin in the case of fish farming.

(207) The aqueous suspensions according to the present invention may be used to produce food for cattle or poultry, and inter alia, as a source of calcium or of calcium and magnesium.

(208) The aqueous suspensions according to the present invention can be used in the paper industry, for example as a component of paper pulp.

(209) They may also be used for sugar refining.

(210) They may also be used to produce precipitated calcium carbonate (PCC).

(211) The present invention also relates to the use of the aqueous solution of calcium hydroxide according to the invention to treat industrial fumes, in particular for desulfurization of the fumes, or to treat household wastewater, in particular potable water, or industrial water.

(212) The present invention also relates to a method for treating gases or fumes comprising a step consisting of injecting/spraying an aqueous solution of slaked lime according to the invention into the gases or fumes to be treated so as to eliminate the acid compounds, sulfur oxides, hydrochloric acids, etc. therefrom.

(213) Another aim of the present invention relates to a method for preparing an aqueous suspension of calcium hydroxide according to the invention.

(214) More specifically, the present invention relates to a method for preparing an aqueous solution of calcium hydroxide, comprising the following steps: a) preparing an aqueous solution containing a copolymer according to the invention, and b) mixing calcium hydroxide in powdered form with said aqueous solution of step a).

(215) According to one embodiment, said method further comprises the step consisting of subjecting the suspension to homogenous shearing.

(216) In the context of the present invention, and according to this embodiment, homogenous shearing results in applying the same minimal mechanical strains for all of the parts of the aqueous suspension mistreated.

(217) According to another embodiment, said method further comprises the step consisting of subjecting the suspension to homogenous shearing with a degree of shearing greater than 50,000 s.sup.1.

(218) Such a degree of shearing makes it possible to obtain a suspension having a high slaked lime content, which does not settle and is stable over time. Applying such a degree of shearing to the suspensions of slaked lime, combined with the use of a hydrosoluble copolymer with a particular chemical structure, therefore makes it possible to achieve these aims. The rheological properties of the resultant dispersion over time are thereby significantly optimized.

(219) According to one embodiment, a homogenous shearing with a degree of shearing greater than 60,000 s.sup.1, in particular greater than 70,000 s.sup.1, is applied. The homogenous shearing required according to this embodiment of the present invention may be obtained according to several alternatives.

(220) According to a first alternative, it is possible to consider subjecting the suspension to a constant shearing rate.

(221) However, the invention is not limited to this particular embodiment.

(222) However, at a given moment, the shearing rate may be different for two points of the suspension. Thus, by varying the geometry of the device used to generate the shearing forces, it is possible to modulate the shearing rate applied to said dispersion in time and/or space.

(223) Because the dispersion is fluid when it undergoes the shearing, each part thereof may thus experience a shearing rate that varies over time. The shearing is said to be homogenous when, irrespective of the variation of the shearing rate over time, it passes through a minimum value that is the same for all parts of the dispersion, at a given moment that may differ from one location of the dispersion to another.

(224) It is possible to consider introducing the suspension of aqueous lime into the shearing device in the form of a whole aqueous suspension (the entire suspension is introduced into the device) or in the form of a primary aqueous suspension (only part of the suspension is introduced into the device).

(225) The shearing device may have varied configurations. The exact configuration is not essential according to the invention inasmuch as at the output of that device, the entire dispersion has undergone the same minimal shearing.

(226) As an illustration, but non-limitingly, devices that may be implemented according to the invention to apply homogenous shearing in particular include the IKA Magic Lab mixer and the Dispax Reactor DR2000.

(227) According to one embodiment of the present invention, a mixer of the rotor-stator type is used to perform said homogenous shearing, for example with a degree of shearing greater than 50,000 s.sup.1.

(228) According to another embodiment, a mixer is used made up of several rotor-stator pairs in direct series.

(229) According to one embodiment of the present invention, a mixer is used made up of cylindrical parts that have a tangential speed greater than 40 m/sec.

(230) A mixer of the rotor-stator type is generally made up of two concentric discs delimiting an enclosure in which the primary dispersion circulates. One of the discs is stationary (stator), and the other is driven by a uniform rotating movement around its axis (rotor). Such a device comprises a supply duct for providing product (in this case, lime suspension) through which the upper disc passes to emerge in the central part of the enclosure. The suspension passes through the air gap formed between the stator and the rotor. The rotor (part of the device driven by a motor) and the stator (stationary part) are respectively made up, on their outer ring, of slits that allow the circulation of the lime suspension to be sheared. Such a device also comprises an output duct connected to a reservoir intended to receive the suspension thus sheared.

(231) The shearing device may comprise a recirculation loop that makes it possible to multiply the passages into the shearing device.

(232) Thus, according to one embodiment, the device used to perform said homogenous shearing is equipped with a recirculation loop.

(233) The method according to any one of the preceding claims, wherein a device configured for a power expenditure of at least 1000 W/m.sup.3 is used to perform said homogenous shearing.

FURTHER EXAMPLES

(234) In all of the trials that follow, the suspensions were evaluated using the parameters described below.

(235) The viscosity (expressed in mPa.Math.s) of the suspension is measured at 20 C. with a Brookfield DVIII-type viscosimeter. The viscosity values indicated are measured before agitation or after agitation, at a speed of 10 rpm and 100 rpm, and at different storage times. The viscosity values after 1 month of storage and after agitation of the suspension (using equipment of the Rayneri type, for example) are particularly relevant to evaluate characteristics of the invention (influence of the polymer, influence of the equipment, influence of the minimum degree of shearing) in light of the use of the suspensions in industrial methods.

(236) The sedimentation of each suspension is evaluated by measuring the height of the deposition in the container. The sedimentation values are expressed in %, i.e., as the ratio of a deposition height to the total height of the suspension in the container, multiplied by 100.

Example 1a

(237) This example illustrates the use of different polymers (prior art, invention, outside invention) in a method for preparing an aqueous suspension of calcium hydroxide (slaked lime) according to the invention.

(238) Several aqueous solutions of calcium hydroxide, each having a solid content of 481%, are prepared in this example. 503 g of water, as well as a quantity of the polymer corresponding to 1.41 wt % dry (based on the total weight of the solids in the suspension), are placed in a container, said polymer being a polymer of the prior art or a polymer according to the present invention. Next, 485 g of slaked lime (Supercalco 97, Carmeuse) is placed in the container with agitation.

(239) An IKA Magic Lab-type mixer adjusted so as to produce shearing of 82,000 s.sup.1 is next supplied with the mixture obtained in the preceding step. A recirculation loop allows several passages in the air gap formed by the rotor and the stator of the IKA mixer.

(240) Once sheared, the suspension is stored so that these viscosity, sedimentation and 1-month stability parameters can be evaluated.

(241) The polymers used in example 1 have the following characteristics:

(242) Test 1-1:

(243) This test illustrates the use, in a method according to the invention, of a homopolymer outside the invention, commercially available under the name Rheosperse 3010, Coatex, France and made up of monomers of acrylic acid, 100% neutralized with sodium hydroxide (molecular weight: 4000 g/mol).

(244) Test 1-2:

(245) This test illustrates the use, in a method according to the invention, of a copolymer outside the invention, commercially available and made up of monomers of acrylic acid and macromonomers with vinyl-PEG.sub.2000 structure, i.e., monomers including 46 units of ethylene oxide.

(246) Thus, this comb polymer does not include monomers of methacrylic acid on the one hand, and units of propylene oxide on the other hand, on its macromonomers.

(247) Test 1-3:

(248) This test illustrates the use, in a method according to the invention, of a copolymer outside the invention, commercially available and made up of 15 wt % of acrylic acid monomers and methacrylic acid monomers, as well as 85 wt % of macromonomers of MPEG.sub.5000 (i.e., methoxy(EO).sub.113 units).

(249) Thus, this comb polymer does not include propylene oxide units on its macromonomers.

(250) Tests 1-4 to 1-8: Copolymers with a Particular Structure, According to the Invention or Outside the Invention

(251) These tests illustrate the use of hydrosoluble copolymers, according to the invention or outside the invention, having: a negatively charged backbone made up of monomers of acrylic acid and/or methacrylic acid, randomly polymerized, and non-charged side chains made up of poly(alkylene glycol) units.

(252) *Test 1-4: Outside Invention

(253) The copolymer has the following composition (in wt % relative to the total weight of the copolymer): 12.8% acrylic acid monomers, 87.2% monomers with formula (I): RXR, wherein R represents a methacrylate function, R designates hydrogen, X represents a structure including 46 units of ethylene oxide EO and 15 units of propylene oxide PO, positioned randomly.

(254) Molecular weight: 38,000-52,000 g/mol

(255) Partial NaOH neutralization; pH: 3-4.5.

(256) This copolymer, which does not include methacrylic acid monomers, is a copolymer outside the invention.

(257) *Test 1-5: According to the Invention

(258) The copolymer has the following composition (in wt % relative to the total weight of the copolymer): 7.44% of methacrylic acid monomers, 92.56% monomers with formula (I): RXR, wherein R represents a methacrylate function, R designates hydrogen, X represents a structure including 46 units of ethylene oxide EO and 15 units of propylene oxide PO, positioned randomly.

(259) Molecular weight: 110,000-150,000 g/mol

(260) Partial NaOH neutralization; pH: 3-4.5.

(261) *Test 1-6: According to the Invention

(262) The copolymer has the following composition (in wt % relative to the total weight of the copolymer): 19.8% methacrylic acid monomers, 3% acrylic acid monomers, and 77.2% monomers with formula (I): RXR, where R represents a methacrylate function, R designates hydrogen, X represents a structure including 46 units of ethylene oxide EO and 15 units of propylene oxide PO, positioned randomly.

(263) Molecular weight: 34,000-44,000 g/mol

(264) Total NaOH neutralization; pH: 7.7.

(265) *Test 1-7: According to the Invention

(266) The copolymer has the following composition (in wt % relative to the total weight of the copolymer): 12.5% methacrylic acid monomers, 87.5% monomers with formula (I): RXR, wherein R represents a methacrylate function, R designates hydrogen, X represents a structure including 46 units of ethylene oxide EO and 15 units of propylene oxide PO, positioned randomly.

(267) Molecular weight: 60,000-95,000 g/mol

(268) Total NaOH neutralization; pH: 6.7-7.7.

(269) *Test 1-8: Outside Invention

(270) The copolymer has the following composition (in wt % relative to the total weight of the copolymer): 24% methacrylic acid monomers, 4.3% acrylic acid monomers, and 71.7% monomers with formula (I): RXR, wherein R represents a methacrylate function, R designates H, X represents a structure including 46 units of ethylene oxide EO.

(271) Neutralization: 100% NaOH

(272) Molecular weight: 17,900 g/mol

(273) This copolymer, whereof the monomers with formula (I) do not include propylene oxide units, is a copolymer outside the invention.

(274) The sedimentation results and various viscosity measurements are shown in table 1 below:

(275) TABLE-US-00006 TABLE 1 viscosity viscosity viscosity viscosity viscosity viscosity afag afag befag befag afag afag Sedimentation T0 T0 T0 + 1 m T0 +1 m T0 + 1 m T0 + 1 m Tests T0 10 rpm 100 rpm 10 rpm 100 rpm 10 rpm 100 rpm 1-1 PA 15% 10 58 1000 124 2770 382 1-2 PA 0 9840 1140 21000 4550 11020 1146 1-3 PA 0 1940 386 17800 3820 7220 1000 1-4 OINV 0 290 170 19000 3310 16460 1900 1-5 INV 0 300 159 4620 890 590 230 1-6 INV 0 250 152 1320 478 730 234 1-7 INV 0 170 114 1260 462 330 170 1-8 OINV 0 30 40 1900 802 470 202 PA: prior art OINV: outside invention INV: invention Afag: after agitation Befag: before agitation

(276) One can first see that the polymers of tests 1-1 (homopolymers of acrylic acid) and 1-8 (copolymers not including propylene oxide and its side chains) do not make it possible to avoid sedimentation. Using these polymers therefore does not make it possible to resolve the technical problem at the origin of the present invention.

(277) The measurement of the viscosity 10 rpm after agitation and at T0 shows that the polymers of tests 1-2 and 1-3 do not make it possible to obtain suspensions of slaked lime having rheological characteristics allowing them to be used in industrial methods, in particular rheological characteristics suitable for pumping of the suspensions. The suspension obtained in test 1-2 using the prior art polymer in fact has a viscosity of 9840 mPa.Math.s at T0 after agitation. The suspension obtained in test 1-3 using another prior art polymer in turn has a viscosity of 1940 mPa.Math.s at T0 after agitation. These values, which are outside the range of claimed viscosities (between 25 and 1000 mPa.Math.s at 20 C.), are incompatible with the expected use of the suspensions.

(278) The measurement of the viscosity 10 rpm after agitation and T0+1 month shows that the polymer of test 1-4 does not make it possible to obtain a concentrated suspension of lime that has a suitable viscosity. In fact, this viscosity is 16,460 s.sup.1.

(279) The rheological profiles of the lime suspensions of tests 1-5, 1-6 and 1-7 (use of a copolymer according to the invention) are suitable for the use of suspensions in industrial methods.

Example 2a

(280) This example illustrates the use of shearing equipment, which may be identical or different, optionally adjusted to different degrees of shearing to prepare an aqueous suspension of calcium hydroxide (slaked lime) containing a copolymer according to the invention.

(281) A first series of three aqueous suspensions of calcium hydroxide (tests 2-1 to 2-3), each having a solid content of 481%, are prepared by placing 503 g of water and a quantity of a polymer that corresponds to 1.41 wt % dry (based on the total weight of the solids in the suspension) in a container. Said polymer is that of test 1-5. Next, 485 g of slaked lime (Supercalco 97, Carmeuse) is placed in the container with agitation.

(282) The second series of three aqueous suspensions of calcium hydroxide (tests 2-4 to 2-6), each having a solid content of 481%, are prepared by placing 503 g of water and a quantity corresponding to 1.41 wt % dry of a polymer (based on the total weight of the solids in the suspension) in a container, said polymer being that of test 1-6. Next, 485 g of slaked lime (Supercalco 97, Carmeuse) is placed in the container with agitation.

(283) Tests 2-1 and 2-4

(284) A mixer of the Ultraturax type (rotor-stator type), adjusted so as to produce shearing of approximately 40,000 s.sup.1 and which procures homogenous shearing according to the definition of the present invention, is supplied with the mixture obtained in the preceding step.

(285) A recirculation loop allows several passages in the mixer. The recirculation time is set at 15 minutes.

(286) Tests 2-2 and 2-5

(287) A mixer of the Rayneri type, adjusted so as to produce shearing of approximately 3000 s.sup.1 (which does not procure homogenous shearing according to the definition of the present invention), is supplied with the mixture obtained in the preceding step.

(288) A recirculation loop allows several passages in the mixer. The recirculation time is set at 15 minutes.

(289) Tests 2-3 and 2-6

(290) A mixer of the IKA Magic Lab type, adjusted so as to produce shearing of 82,000 s.sup.1 and which procures homogenous shearing according to the definition of the present invention, is then supplied with the mixture obtained in the preceding step.

(291) A recirculation loop allows several passages in the air gap formed by the rotor and stator of the IKA mixer. The recirculation time is set at 15 minutes.

(292) Once sheared, the suspensions are stored for evaluation of the viscosity, sedimentation, and 1-month stability month parameters.

(293) The results for sedimentation and various viscosity measurements are provided in table 2 below:

(294) TABLE-US-00007 TABLE 2 viscosity viscosity viscosity viscosity viscosity viscosity afag afag befag befag afag afag Sedimentation T0 T0 T0 + 1 m T0 + 1 m T0 + 1 m T0 + 1 m Tests T0 10 rpm 100 rpm 10 rpm 100 rpm 10 rpm 100 rpm 2-1 OINV 30% 70 107 3300 560 430 168 2-2 OINV 20% 50 98 2400 236 790 220 2-3 INV 0 300 159 4620 890 590 230 2-4 OINV 30% 650 162 1600 580 1890 380 2-5 OINV 30% 260 107 19300 1800 1000 240 2-6 INV 0 250 152 1320 478 730 234 OINV: outside invention INV: invention Afag: after agitation Befag: before agitation

(295) One can first see that the degree of shearing used in tests 2-1 and 2-4 (Ultraturax adjusted to 40,000 s.sup.1) and tests 2-2 and 2-5 (mixer 3000 s.sup.1) does not make it possible to avoid sedimentation.

(296) However, the degree of shearing of tests 2-3 and 2-6 (IKA adjusted to 82,000 s.sup.1), combined with the use of the polymer with a particular structure, makes it possible not only to avoid the problem of sedimentation, but also to obtain suspensions whereof the rheological profile is suitable for the expected use.

Example 3a

(297) This example illustrates the use of two polymers according to the invention in a method for preparing an aqueous solution of calcium hydroxide (slaked lime) with a high content of dry matter (>50 wt %).

(298) Two aqueous suspensions of calcium hydroxide, each having a solid content of 50 to 51%, are prepared in this example. 478 g of water, as well as a quantity corresponding to 1.41 wt % dry of a polymer, based on the total weight of the solids in the suspension, are placed in a container. Next, 505 g of slaked lime (Supercalco 97, Carmeuse) is placed in the container with agitation.

(299) A mixer of the IKA Magic Lab type, adjusted so as to produce shearing of 82,000 s.sup.1, is next supplied with the mixture obtained in the preceding step. A recirculation loop allows several passages in the air gap formed by the rotor and the stator of the IKA mixer.

(300) Once sheared, the suspension is stored for evaluation of its viscosity, sedimentation, and 1-month stability parameters.

(301) The polymers used in this example have the following characteristics:

(302) Test 3-1: According to the Invention

(303) The copolymer has the following composition (in wt % relative to the total weight of the copolymer): 7.44% methacrylic acid monomers, 92.56% monomers with formula (I): RXR, wherein R represents a methacrylate function, R designates hydrogen, X represents a structure including 46 units of ethylene oxide EO and 15 units of propylene oxide PO, positioned randomly.

(304) Molecular weight: 110,000-150,000/gmol

(305) Partial NaOH neutralization; pH: 3-4.5.

(306) Test 3-2: According to the Invention

(307) The copolymer has the following composition (in wt % relative to the total weight of the copolymer): 19.8% monomers of methacrylic acid, 3% monomers of acrylic acid, and 77.2% monomers with formula (I): RXR, wherein R represents a methacrylate function, R designates hydrogen, X represents a structure including 46 units of ethylene oxide EO and 15 units of propylene oxide PO, positioned randomly.

(308) Molecular weight: 34,000-44,000 g/mol

(309) Total NaOH neutralization; pH: 7.7.

(310) The results for sedimentation and various viscosity measurements are shown in table 3 below:

(311) TABLE-US-00008 TABLE 3 viscosity viscosity viscosity viscosity viscosity viscosity afag afag befag befag afag afag Sedimentation T0 T0 T0 + 1 m T0 + 1 m T0 + 1 m T0 + 1 m Tests T0 10 rpm 100 rpm 10 rpm 100 rpm 10 rpm 100 rpm 3-1 50.4% lime 0% 980 393 4900 1980 1930 687 3-2 50.56% lime 0% 530 261 13600 3048 3300 839 Afag: after agitation Befag: before agitation

(312) The results demonstrate that it is possible, using the method according to the present invention, and using hydrosoluble copolymers with a particular structure, to prepare suspensions of slaked lime with a high concentration that remain stable over time.

Example 4a

(313) This example illustrates the use of two polymers according to the invention in a method for preparing an aqueous suspension of calcium hydroxide from two different types of starting slaked lime, i.e., a lime having a mean particle diameter between 4 and 5 m (Supercalco 97, Carmeuse) and a lime having a mean particle diameter between 2 and 3 m (Supercalco 97/20, Carmeuse).

(314) Several aqueous suspensions of calcium hydroxide, each having a solid content of 481%, are prepared in this example. 503 g of water, as well as a quantity corresponding to 1.41 wt % dry of a polymer (based on the total weight of the solids in the suspension), are placed in a container. Next, 485 g of slaked lime, specifically Supercalco 97 (Carmeuse) in tests 4-1 and 4-3, or Supercalco 97/20 (Carmeuse) in tests 4-2 and 4-4, is placed in the container with agitation.

(315) A mixer of the IKA Magic Lab type, adjusted so as to produce a shearing of 82,000 s.sup.1, is next supplied with the mixture obtained in the preceding step.

(316) A recirculation loop allows several passages in the air gap formed by the rotor and the stator of the IKA mixer.

(317) Once sheared, the suspension is stored for evaluation of these viscosity, sedimentation, and 1-month stability parameters.

(318) The polymers used in this example have the following characteristics:

(319) Tests 4-1 and 4-2: According to the Invention

(320) The copolymer has the following composition (in wt % relative to the total weight of the copolymer): 7.44% monomers of methacrylic acid, 92.56% monomers with formula (I): RXR, wherein R represents a methacrylate function, R designates hydrogen, X represents a structure including 46 units of ethylene oxide EO and 15 units of propylene oxide PO, positioned randomly.

(321) Molecular weight: 110,000-150,000 g/mol

(322) Partial NaOH neutralization; pH: 3-4.5.

(323) Tests 4-3 and 4-4: According to the Invention

(324) The copolymer has the following composition (in wt % relative to the total weight of the copolymer): 19.8% monomers of methacrylic acid, 3% monomers of acrylic acid, and 77.2% monomers with formula (I): RXR wherein R represents a methacrylate function, R designates hydrogen, X represents a structure including 46 units of ethylene oxide EO and 15 units of propylene oxide PO, positioned randomly.

(325) Molecular weight: 34,000-44,000 g/mol

(326) Total NaOH neutralization; pH: 7.7.

(327) The results for sedimentation and different viscosity measurements are shown in table 4 below:

(328) TABLE-US-00009 TABLE 4 viscosity viscosity afag afag Sedimentation T0 T0 Tests T0 10 rpm 100 rpm 4-1 INV 0% 300 159 4-2 INV 0% 280 203 4-3 INV 0 250 152 4-4 INV 0% 190 126 Afag: after agitation Befag: before agitation

(329) The results demonstrate that it is possible, according to the method of the present invention, using hydrosoluble copolymers with a particular structure, to prepare suspensions of slaked lime with a high concentration remaining stable over time, irrespective of the initial particle size of the slaked lime.

Example 5a

(330) The purpose of this example is to illustrate the total organic carbon (TOC) levels present in the aqueous phase of the lime suspensions dispersed with the polymers of the prior art or with polymers according to the invention, and thereby to determine the free polymer concentrations in the aqueous phase.

(331) This example also makes it possible to illustrate the soluble Ca.sup.2+ ion content levels present in the aqueous phase of the lime suspensions dispersed with the polymers of the prior art or with the polymers according to the invention.

(332) Method for Preparing the Suspensions

(333) Several aqueous suspensions of calcium hydroxide, each having a solid content of 481%, are prepared in this example. 503 g of water, as well as a quantity corresponding to 1.41 wt % dry of a polymer (based on the total weight of the solids in the suspension), are placed in a container, said polymer being according to the prior art or the present invention. Next, 485 g of slaked lime (Supercalco 97, Carmeuse) is introduced into the container with agitation.

(334) A mixer of the IKA Magic Lab type, adjusted so as to produce shearing of 82,000 s.sup.1, is then supplied with the mixture obtained in the preceding step. A recirculation loop allows several passages in the air gap formed by the rotor and the stator of the IKA mixer.

(335) Test 5-1

(336) The copolymer has the following composition (in wt % relative to the total weight of the copolymer): 7.44% monomers of methacrylic acid, 92.56% monomers with formula (I): RXR, wherein R represents a methacrylate function, R designates hydrogen, X represents a structure including 46 units of ethylene oxide EO and 15 units of propylene oxide PO, positioned randomly.

(337) Molecular weight: 110,000-150,000 g/mol

(338) Partial NaOH neutralization; pH: 3-4.5.

(339) Test 5-2

(340) The copolymer has the following composition (in wt % relative to the total weight of the copolymer): 12.8% monomers of acrylic acid, 87.2% monomers with formula (I): RXR, wherein R represents a methacrylate function, R designates hydrogen, X represents a structure including 46 units of ethylene oxide EO and 15 units of propylene oxide PO, positioned randomly.

(341) Molecular weight: 38,000-52,000 g/mol

(342) Partial NaOH neutralization; pH: 3-4.5.

(343) This copolymer, which does not include methacrylic acid monomers, is a copolymer outside the invention.

(344) Test 5-3

(345) The polymer used is a homopolymer outside the invention, commercially available under the name Rheosperse 3010, Coatex, France and made up of monomers of acrylic acid, 100% neutralized with sodium hydroxide (molecular weight: 4000 g/mol).

(346) The obtained suspensions are filtered.

(347) A sample of the filtrate is withdrawn and analyzed using the methods described below.

(348) TOC Measurement:

(349) The TOC (Total Organic Carbon) is measured using a Shimadzu TOC-V CSH, using a method based on a catalytic oxidation method by combustion at 680 C.

(350) The carbon atoms of the samples are oxidized in CO.sub.2. The eluent gas pushes the CO.sub.2 into a system allowing the elimination of the H.sub.2O molecules and halogenated compounds. An IR (infrared) detector measures the CO.sub.2 concentration. A calibration curve makes it possible to determine the carbon concentration in the sample.

(351) Ion Assaying:

(352) The ion content is evaluated using ion chromatography by using Metrohm 761 Compact IC-type equipment. The separation of the ions and the polar molecules is based on their charge.

(353) The results of the TOC and free Ca.sup.2+ ion content level measurements are provided in table 5 below:

(354) TABLE-US-00010 TABLE 5 polymer Ca2+ TOC concentration Tests ppm ppm ppm 5-1 INV 1064 1640 396 5-2 OINV 995 3900 856 5-3 PA 291 100 17 OINV: outside invention INV: invention PA: prior art

(355) It is first possible to see that the free Ca.sup.2+ ion content levels vary significantly based on the nature of the polymer used. This free Ca.sup.2+ ion content level in a lime suspension dispersed with an acrylic acid homopolymer (test 5-3) is low compared to that of an aqueous lime suspension dispersed with a copolymer having a methacrylic acid backbone and poly(alkylene glycol) side chains (tests 5-1 and 5-2).

(356) Furthermore, although the quantities of starting polymer (1.41 wt % dry) are identical for each of the suspensions, it is noted that the polymer concentrations in the filtrate of each suspension vary significantly based on the polymer used. When the polymer used is an acrylic acid homopolymer, the concentration of soluble polymer in the aqueous phase is practically nonexistent. Furthermore, less free copolymer remains in the filtrate of the lime suspension when a copolymer according to the invention is used. Without being bound by any theory, one may think that the particular structure of the copolymer according to the invention is suited to the chemical nature of the lime, which improves the chemical interactions between the copolymer and the Ca(OH).sub.2 particles. There are fewer free copolymers in the lime suspensions prepared using the inventive method by using a copolymer with a particular structure, since a larger quantity thereof is adsorbed to the surface of the slaked lime particles. It has thus been demonstrated that subjecting a concentrated aqueous suspension of lime to a shearing operation under specific conditions in the presence of a copolymer according to the invention makes it possible to obtain a concentrated, stable lime suspension that is novel relative to the lime suspensions of the prior art, due to the particular chemical interactions between the copolymers and the lime particles.

(357) Embodiment 1a. A use of a hydrosoluble copolymer made up of: monomers of methacrylic acid and/or any one of its salts, optionally, monomers of acrylic acid and/or any one of its salts, monomers with formula (I):
RXR (I) wherein: R represents a polymerizable unsaturated function, in particular acrylate, methacrylate, methacryl-urethane, vinyl or allyl, R designates hydrogen or an alkyl group having from 1 to 4 carbon atoms, X represents a structure including n unit(s) of ethylene oxide EO and m unit(s) of propylene oxide PO, positioned randomly or regularly, m and n are two non-zero integers and comprised between 1 and 150, to prepare an aqueous suspension of calcium hydroxide from powdered calcium hydroxide.

(358) Embodiment 2a. An aqueous suspension of calcium hydroxide, comprising at least one copolymer made up of: monomers of methacrylic acid and/or any one of its salts, optionally, monomers of acrylic acid and/or any one of its salts, monomers with formula (I):
RXR (I) wherein: R represents a polymerizable unsaturated function, in particular acrylate, methacrylate, methacryl-urethane, vinyl or allyl, R designates hydrogen or an alkyl group having from 1 to 4 carbon atoms, X represents a structure including n unit(s) of ethylene oxide EO and m unit(s) of propylene oxide PO, positioned randomly or regularly, m and n are two non-zero integers and comprised between 1 and 150.

(359) Embodiment 3a. The use according to Embodiment 1a or the suspension according to claim 2, wherein said suspension has a dry content of at least 40 wt %.

(360) Embodiment 4a. The use or suspension according to any one of the preceding Embodiments 1a-3a, wherein the viscosity of said aqueous suspension measured by a Brookfield DVIII viscosimeter at 10 rpm is comprised between 25 and 1000 mPa.Math.s at 20 C.

(361) Embodiment 5a. The use or suspension according to any one of the preceding Embodiments 1a-4a, wherein the copolymer has a molecular weight comprised between 30,000 and 200,000 g/mol as determined by steric exclusion chromatography (SEC).

(362) Embodiment 6a. The use or suspension according to any one of the preceding Embodiments 1a-4a, wherein said monomer of formula (I) is such that n and m are two non-zero integers and n+m>17.

(363) Embodiment 7a. The use or suspension according to any one of the preceding Embodiments 1a-6a, wherein the function R of said monomer with formula (I) represents the methacrylate function.

(364) Embodiment 8a. The use or suspension according to any one of the preceding Embodiments 1a-7a, wherein the function R of said monomer with formula (I) represents H or CH.sub.3.

(365) Embodiment 9a. The use or suspension according to any one of the preceding Embodiments 1a-8a, wherein said monomer with formula (I) is made up of, expressed in percentage by weight of each of its components: 5 to 30 wt % monomers of methacrylic acid and/or any one of its salts, 0 to 10 wt % monomers of acrylic acid and/or any one of its salts, 70 to 95 wt % monomers with formula (I).

(366) Embodiment 10a. The use of the aqueous suspension of calcium hydroxide according to any one of Embodiment 1a, 3a to 9a, to treat industrial fumes, in particular for desulfurization of the fumes, or to treat household wastewater, in particular potable water, or industrial water.

(367) Embodiment 11a. A method for preparing an aqueous solution of calcium hydroxide, comprising a step consisting of subjecting the suspension to homogenous shearing.

(368) Embodiment 12a. The method according to Embodiment 11a, wherein homogenous shearing is applied with a degree of shearing greater than 50,000 s.sup.1.

(369) Embodiment 13a. The method according to Embodiment 11a or 12a, wherein a mixer of the rotor-stator type is used to perform said homogenous shearing.

(370) Embodiment 14a. The method according to any one of Embodiments 11a to 13a, wherein the device used to perform said homogenous shearing is equipped with a recirculation loop.

(371) Embodiment 15a. The method according to any one of Embodiments 11a to 14a, wherein a device configured for a power expenditure of at least 1000 W/m.sup.3 is used to perform said homogenous shearing.